Bugs

When placing blocks it is possible to phase through them and fall to the core of the planet.
When leaving an area chunks have the possibility to reset to their unmodified form
When leaving an area chests can lose the items stored inside. One way to mitigate is to only have one chest per chunk.
Sometimes when teleporting gravity can get messed up.
Switching graphics setting can cause visual bugs
Torch flame particles can sometimes spawn floating in the air
Mobs can sometimes rotate in strange ways
Trees sometimes don't generate properly when generating along chunk boarders
Holding crouch and then destroying the block you are standing on can leave the player floating
Sometimes clicking doesn't register